Horse Sweet Itch Genetic Basis | Animal Welfare Hub

Sweet itch has a significant heritable component, and understanding the genetic basis of Culicoides hypersensitivity may enable breeding selection to reduce disease prevalence in susceptible populations.

Key Facts

Twin studies and family clustering data suggest a heritable component to sweet itch susceptibility
Icelandic horses are particularly susceptible to sweet itch after importation to areas with Culicoides midges
Specific MHC haplotypes have been associated with sweet itch risk in some breed studies
The condition does not manifest in Iceland where the relevant Culicoides species are absent
Breeding selection against sweet itch is complicated by the lack of a reliable pre-exposure genetic test
Research into genetic markers associated with immune response dysregulation in sweet itch is ongoing

Welfare Considerations

The heritable component of sweet itch means that breeding decisions have direct welfare implications for future generations of horses. Horses from lines with high sweet itch prevalence face elevated probability of suffering the chronic and recurrent pruritus that characterises the condition. While no validated pre-exposure genetic test currently allows definitive breeding selection against susceptibility, breed societies can promote awareness of family history and encourage breeding from lines with lower prevalence. Genetic research that identifies reliable markers could enable selection to reduce the proportion of future horses facing this welfare burden.

What You Can Do

Consider sweet itch history in both sire and dam lines when making breeding decisions
Engage with breed societies about recording and sharing sweet itch prevalence data across bloodlines
Support equine genetic research into immune response genes associated with sweet itch susceptibility
Inform purchasers of offspring from sweet itch-affected lines about the elevated risk
Advocate for breed registration schemes to include health data collection for hereditary conditions